To measure a blood glucose level, a method is employed which uses a blood glucose level measurer and a biosensor in combination (See Patent Document 1, for example). As the biosensor, use may be made of one having the structure shown in FIGS. 3-6. The illustrated biosensor 2 is designed to measure the blood glucose level by an electrochemical technique and includes a capillary 23 and electrodes 25 and 26. In the capillary 23, a reagent portion 28 is provided. When blood is introduced into the capillary, the capillary provides a reaction field for reaction between the blood and a reagent contained in the reagent portion 28. The electrodes 25 and 26 are utilized for applying a voltage to the reaction field and measuring the response current obtained by the voltage application.
The sensitivity of the biosensor 2 may vary according to the manufacturing factory or the manufacturing line. Therefore, in a blood glucose level measurer, a plurality of calibration curves are stored in advance, and the calibration curve suitable for the sensitivity of the biosensor is selected. The blood glucose level is computed based on the selected calibration curve and the response current. The selection of the calibration curve may be performed manually by the user. As an alternative method, the selection of the calibration curve corresponding to the sensitivity of the biosensor 2 may be performed by making the blood glucose level measurer detect the existence or absence of a through-hole 24a at a recognition target portion 24 of the biosensor 2. Specifically, as will be understood from FIGS. 9A and 9B, detection terminal pairs 11 and 12 in the form of a leaf spring are provided in the blood glucose level measurer 1, and the existence or absence of the through-hole 24a is recognized by detecting whether or not the terminals 11A, 11B, 12A, 12B of the detection terminal pairs 11, 12 are in contact with each other when the biosensor 2 is mounted to the blood glucose level measurer 1.
In normal conditions, when the biosensor 2 is not mounted to the blood glucose level measurer 1, the terminals 11A and 11B (12A and 12B) of the detection terminal pair 11, 12 are in contact with each other. However, one terminal 11A, 12A of the detection terminal pair 11, 12 is in the form of a leaf spring, and its elasticity is reduced due to the repetitive use. Therefore, the terminals 11A and 11B (12A and 12B) may not come into contact with each other although the biosensor 2 is not mounted to the blood glucose level measurer 1. In such a case, as shown in FIG. 11 for example, the terminals 11A and 11B (12A and 12B) of the detection terminal pair 11 (12) do not come into contact with each other even when the through-hole 24a is formed at the recognition target portion 24. When this situation occurs, the blood glucose level measurer 1 determines that the through-hole 24a is not formed at the recognition target portion 24a and selects a wrong calibration curve. As a result, the blood glucose level obtained by the blood glucose level measurer 1 deviates from the correct value.    Patent Document 1: JP-B-H08-10208